Charles Wesley was a prolific hymn writer, penning over 6000 hymns, more than any other male writer. (19th century blind lyricist Fanny Crosby wrote over 8000). He had the ability of expressing sublime truth in simple ways, his motivation in writing his hymns being to teach the poor and illiterate good doctrine. Wesley's brother, John, said that Charles hymnal was the best theological book in existence. It is said Methodism was born in song and Charles was the chief songwriter. Amongst the other hymns Charles Wesley wrote were, "O For A Thousand Tongues" and "Jesus, Lover of my Soul."
Wesley got the idea for this hymn from a popular song of the day, "Fairest Isle, All Isles Excelling" - part of a semi-opera about King Arthur by John Dryden set to music by Henry Purcell. Whilst the tune provided the music and metre for the hymn, the words concern divine love, not the pagan one of Dryden's lyric. The hymn first appeared in Wesley's 1747 collection Hymns for those that seek, and those that have Redemption.
This is a frequent choice of hymn for a wedding service. It's celebration of divine love making it suitable as the first hymn praising God in whose presence everyone has assembled. Alternatively it suitable as the second hymn sung after the marriage ceremony in praise and celebration of the union.